Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 141153
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
553 AM CST Thu Dec 14 2017

...Update to aviation forecast discussion...

.SHORT TERM...(Today and tonight)
Issued at 301 AM CST Thu Dec 14 2017

Current WV imagery suggests that the Pacific ridge remains highly
amplified over the western CONUS. Northwest flow aloft generally
remains over the Plains region with a broad trough over the Great
Lakes into the Mid Atlantic and New England regions. Yesterdays
low pressure system has lifted into the eastern portions of the
Great Lakes. A remnant diffuse cold front is now draped through
the Ohio Valley back into northern Texas. Two notable shortwaves
are now over the WY/CO border and another diving down from Central
Canada into the northern Plains. The shortwave advancing into the
northern Plains is a compact wave and doesn`t have a strong
influence on surface weather conditions at the moment with only a
couple spots in the Dakotas reporting light snow. The shortwave
over the Rockies remains an open wave and has a broad expanse of
cloud cover within and area of ascent over the mountains with some
high clouds extending over northeast Kansas. Additionally some
low level cold air stratus has moved into the area from the north.

Lows early this morning hold into the upper 20s with the cloud cover
moving into the region.  Today, the aforementioned shortwaves impact
the region with the northern Plains wave essentially dampening out
as it phases with a larger vort lobe extending through the central
Plains into the Desert Southwest region.  Sounding profiles and
ensemble data suggest precip amounts that do occur today will be
minimal with mostly rain early in the afternoon and then into the
evening transitioning to a rain snow mix as the lower levels cool
throughout the day via web bulb effects. Again, lift is generally
weak, so amounts should remain on the low end of guidance.  Only
have generally 0.01 to 0.04" of QPF amounts mainly north of I-70.
Areas that do actually see snow should only have a very light
dusting with any real measurable amounts hard to come by. Nearly all
hi-res short-term guidance is in favor of light amounts of possible
snow fall later when the transition does occur with WRF members
being slightly higher than HRRR and RAP guidance.  All remain under
0.5" accumulations at the most.  Highs during the day should top out
in the low 40s with lows over night settling in the mid 20s as
clouds begin to clear.

.LONG TERM...(Friday through Wednesday)
Issued at 301 AM CST Thu Dec 14 2017

There continues to be a chance for precip late Saturday night and
into Sunday morning. There is pretty good agreement among the
various solutions for a shortwave to eject northeast from northern
Mexico into southern MO. The better forcing still looks to pass
mainly to the southeast of the forecast area. And models are
showing the deeper moisture possibly clipping east central KS, but
generally remaining southeast as well. What moisture return there
is further north Saturday night appears to be shallow and
forecast soundings fail to saturate the dendritic growth zone for
there to be any ice in the column. Because of this, there is some
potential for mixed precip across parts of north central and
northeast KS where morning lows dip below freezing. This potential
looks to be confined to the mid morning hours as temps diurnally
warm above freezing. And with these areas further removed from the
better forcing and moisture, accumulations would be light. At
this point chances are about 20 to 30 percent for the mixed precip
with POPs increasing into east central KS. However will need to
watch this potential over the coming days as freezing rain would
create a hazard for a brief period of time Sunday morning. Across
east central KS where there are higher POPs, temps look to be
warmer as models have slowed down a cold front. Lows are expected
to be in the mid and upper 30s allowing for just a cold rain if
there is precip Sunday morning.

The initial shortwave passes to the east of the area by Sunday
morning. However a weak frontal boundary and elongated upper
trough are progged to remain over the central plains. There is
some variability in the models, but a few generate some light
precip along the frontal boundary Sunday night over east central
KS. Because of the have some small POPs in the forecast. Again
chances are small but if there is precip as temps drop to or below
freezing, there could be some mixed precip. This upper trough
shears out and gives wave to weak upper ridging by Monday night.
There may be a cutoff low formed from energy in the base of the
upper trough. For now all the models keep this feature to the
south. So the forecast is for dry weather Monday through Wednesday
with moderate temps.

For temps, above normal readings are likely Friday and Saturday.
Models show 925MB temps warming to near 10C with reasonable
insolation on Friday and Saturday. Have increased highs across
north central KS Friday where good mixing could bring these warmer
925MB temps to the surface, and I may still be on the cool side.
Highs Saturday look to be in the upper 50s and lower 60s as the
thermal ridge moves into northeast KS. With clouds and precip
possible, highs Sunday should be cooler with readings in the 40s.
After Sunday, there may be some weak cold air advection on
Tuesday. So moderate temps with lower around 30 and highs in the
50s are expected for Monday through Wednesday.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 537 AM CST Thu Dec 14 2017

Keeping the 12Z TAFs VFR for now. There is some indication there
could be a general lowering of the CIGS this afternoon and
evening. Chances for precip remain too low to mention. Winds
remain unidirectional for the period and generally light. Expect
clearing of low clouds by the end of the period.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Drake
LONG TERM...Wolters
AVIATION...Drake



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